Characterization of In-Cylinder Techniques for Thermal Management of Diesel Aftertreatment

One challenge in meeting emission regulations with catalytic aftertreatment systems is maintaining the proper catalyst temperatures that enable the catalytic devices to perform the emissions reduction. In this study, in-cylinder techniques are used to actively control the temperature of a catalyzed diesel particulate filter (DPF) in order to raise the DPF temperature to induce particulate oxidation. The performance of four strategies is compared for two different starting DPF temperatures (150°C and 300°C) on a 4-cylinder 1.7-liter diesel engine. The four strategies include: (1) addition of extra fuel injection early in the combustion cycle for all four cylinders, (2) addition of extra fuel injection late in the combustion cycle for all four cylinders, (3) operating one-cylinder with extra fuel injection early in the combustion cycle, and (4) operating one-cylinder with extra fuel injection late in the combustion cycle. In cases (3) and (4), the cylinder operating with extra fuel injection is changed frequently to avoid oil dilution complications. In addition to the in-cylinder strategies, an in-pipe fuel addition technique for thermal management was studied for comparison. Results show that at starting temperatures above 300°C, late cycle injection strategies that cause temperature rise from exotherms created by unburned fuel components result in higher temperature rise for a given fuel penalty. At the low temperature of 150°C, early injection strategies that create temperature rise from both combustion and light reductant exotherms are preferred due to the inability of the catalyst to oxidize unburned fuel from late injection strategies.